Advance polls and the "late switch" in the 2004 election.

• Author: Kay, Barry J.

Every election produces considerable discussion among pollsters, academics and politicians about the accuracy of pre-election polls. One analytical tool that has previously received little academic attention is the impact of voting in the advance polls. In 2004 they were held on June 18, 19 and 21 with the general election on June 28. Does public opinion change dramatically during the campaign's final days? This article seeks to address two questions. Are advance poll voters reflective of the broader range of the Canadian electorate at the time they occur? Did advance poll voters in 2004 perform distinctively enough from the general election voters so as to suggest a systematic change during the final days of the campaign?

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Perhaps nobody was more surprised by the election night results of Canada's federal vote on June 28, 2004 than the array of pollsters who had been consulted at regular intervals during the preceding campaign. It was not that the Canadian public had been free of volatility. In fact the election campaign had taken on the proportions of a roller coaster ride for much of its duration. For example, in the key swing province of Ontario, a weighted aggregation of polls indicated the Liberals dropping from a 23% lead over the Conservatives in the period ending May 15, a week before the writs were dropped, to a 2% deficit to the Conservatives five weeks later on June 18, only to have the Liberals rebound to a 13% advantage on election night. (1)

Rather the reason for the surprise among practitioners of the public opinion industry, was the remarkable consistency that had been demonstrated in the set of polls released during the week prior to election day. Table 1 shows the results of seven separate polls published by six different polling companies during the final week of the campaign. They were based upon interviews conducted from June 17 through June 24.

The discrepancy between these figures and the actual results, led to a round of articles following the election by eager skeptics in the press about how the pollsters got it wrong. (2) While pollster error is always a possibility, there are other explanations to be considered for the inconsistency between late polls and the final election results in 2004. This is particularly so after a substantially better record by late polls in other recent federal votes. (3) The most obvious alternate hypothesis to pollster error was that public opinion, at least in certain regions of the country, might have been subject to late volatility after the polling for pre-election reports had ended on June 24.

There were in fact other sources of evidence available from two companies that remained in the field, following the last round of pre-election poll releases. Ipsos-Reid reported a spike for the Liberals on election eve, Sunday, June 27, of approximately 15% over the preceding days in Ontario. (4) This observation was based upon a relatively small sample, but it did portend the findings of an election day poll undertaken by Compas for Global Television. (5)

The election day survey was drawn from a sample of 1200, and one of its most striking features was 21.8% reporting that they made their voting decision on election day. These data are presented in Table 2, which also shows that over 40% of the sample had decided on their choice during the last week. It was further reported that of those deciding during the final week of the campaign, 45% voted Liberal. (6) It can be deduced from the statistic, that among those deciding before the final week, only 31% of the sample voted Liberal. Within this remarkable degree of late choice for the Liberals, would seem to lie an explanation as to why the polls reported in Table 1 understated the Liberal vote. Much of the change occurred, after they left the field.

Advance Poll Results

Another way to approach this issue is to analyze the advance poll results. As a rarely utilized research...